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Full text of "Alaskan glacier studies of the National Geographic Society in the Yakutat Bay, Prince William Sound and lower Copper River regions"

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Toward the north, on the other hand, in the region dominated by the northern arm of the Hubbard, the condition is wholly different. Crevasses appear, the moraine no longer forms a continuous cover but exists in ribbons with intervening areas of relatively clean ice»- and in a very few yards the glacier surface becomes quite impassable. Beyond lies the great sea of clean, white, crevassed and pinnacled ice, contrasting strikingly with the undulating black moraine of the Variegated Glacier. There is much variety in detail in this zone of actively-moving marginal ice of the Hubbard. For example, at one point the broken ice forms a pronounced dirt-covered ridge rising above the neighboring clear ice. Here the layers are steeply-inclined, and it is evident that lower debris-charged layers have been upturned and that the debris has so protected the broken ice from ablation that it stands up as a prominent, crevassed ridge. Here and there are small ponds on the ice surface, and everywhere there is great variety in the crevassing. One very notable feature in 1905 was the presence of a saucer-shaped depression, fully 250 yards in diameter and 100 feet deep, in the actively-moving, crevassed ice, giving a local down-stream ascent to a part of the glacier surface just beyond the steep descent from the mountain valley. There are other undulations of the marginal surface which are interpreted as indications that the glacier is flowing over an irregular bottom.
From this description the relations of the Hubbard and Variegated Glaciers are clear. They coalesce for some distance, but each maintains its individuality in all but a very narrow strip, and one is vigorously active, the other quite stagnant. It is a question whether the united ice mass from the northwestern margin of the Hubbard to the southeastern margin of the Variegated ice bulb should be considered as one piedmont glacier. In a sense this is a warranted interpretation of the phenomena, and both Russell and Gilbert adopted this interpretation, and extended the name Hubbard Glacier to include not only the actively-moving ice but also the stagnant Variegated bulb. We are inclined, however, to confine the name Hubbard to the part dominated by the vigorous north and northwest arms, and apply the name Variegated to the stagnant piedmont bulb which it has formed, because the two glaciers are so different in character, and «ach portion is completely formed and dominated from a different source. At the same time, we recognize the fact that this entire low-lying ice mass, outside the individual valleys from which the supplying glaciers issue, is a continuous ice plateau, analogous to a piedmont glacier, though itself within a mountain valley. In this sense it might be warranted to give a name to the ice plateau, as in the case of Malaspina Glacier, and to give separate names to the three contributing glaciers—the northwest arm, the north arm, and the Variegated. A fourth glacier, the Orange, which barely coalesces with the Variegated, is to be classed with this system. Certainly at no very distant date, as is proved by the high-lying moraine terrace and the marginal drainage channels, these four glaciers contributed to the formation of a great trunk glacier which flowed out into Russell Fiord and Disenchantment Bay; but now recession has proceeded so far that the two eastern arms are so separated from the Hubbard that we believe it best in accordance with the facts to treat them as separate glaciers down to their terminus.
The third portion of the southeastern margin of Hubbard Glacier is the outermost part, beyond the point where the glacier turns so far to the west that it is again separated completely from the Variegated bulb. In this portion the two glaciers are separated by a V-shaped valley in whose bottom a small, branching glacial stream flows, depositing out-wash gravels (PL XLIX). From the sea to the head of the valley the distance is about